ssh_config.0 revision 262566
1SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5) 2 3NAME 4 ssh_config - OpenSSH SSH client configuration files 5 6SYNOPSIS 7 ~/.ssh/config 8 /etc/ssh/ssh_config 9 10DESCRIPTION 11 ssh(1) obtains configuration data from the following sources in the 12 following order: 13 14 1. command-line options 15 2. user's configuration file (~/.ssh/config) 16 3. system-wide configuration file (/etc/ssh/ssh_config) 17 18 For each parameter, the first obtained value will be used. The 19 configuration files contain sections separated by ``Host'' 20 specifications, and that section is only applied for hosts that match one 21 of the patterns given in the specification. The matched host name is the 22 one given on the command line. 23 24 Since the first obtained value for each parameter is used, more host- 25 specific declarations should be given near the beginning of the file, and 26 general defaults at the end. 27 28 The configuration file has the following format: 29 30 Empty lines and lines starting with `#' are comments. Otherwise a line 31 is of the format ``keyword arguments''. Configuration options may be 32 separated by whitespace or optional whitespace and exactly one `='; the 33 latter format is useful to avoid the need to quote whitespace when 34 specifying configuration options using the ssh, scp, and sftp -o option. 35 Arguments may optionally be enclosed in double quotes (") in order to 36 represent arguments containing spaces. 37 38 The possible keywords and their meanings are as follows (note that 39 keywords are case-insensitive and arguments are case-sensitive): 40 41 Host Restricts the following declarations (up to the next Host or 42 Match keyword) to be only for those hosts that match one of the 43 patterns given after the keyword. If more than one pattern is 44 provided, they should be separated by whitespace. A single `*' 45 as a pattern can be used to provide global defaults for all 46 hosts. The host is the hostname argument given on the command 47 line (i.e. the name is not converted to a canonicalized host name 48 before matching). 49 50 A pattern entry may be negated by prefixing it with an 51 exclamation mark (`!'). If a negated entry is matched, then the 52 Host entry is ignored, regardless of whether any other patterns 53 on the line match. Negated matches are therefore useful to 54 provide exceptions for wildcard matches. 55 56 See PATTERNS for more information on patterns. 57 58 Match Restricts the following declarations (up to the next Host or 59 Match keyword) to be used only when the conditions following the 60 Match keyword are satisfied. Match conditions are specified 61 using one or more keyword/criteria pairs or the single token all 62 which matches all criteria. The available keywords are: exec, 63 host, originalhost, user, and localuser. 64 65 The exec keyword executes the specified command under the user's 66 shell. If the command returns a zero exit status then the 67 condition is considered true. Commands containing whitespace 68 characters must be quoted. The following character sequences in 69 the command will be expanded prior to execution: `%L' will be 70 substituted by the first component of the local host name, `%l' 71 will be substituted by the local host name (including any domain 72 name), `%h' will be substituted by the target host name, `%n' 73 will be substituted by the original target host name specified on 74 the command-line, `%p' the destination port, `%r' by the remote 75 login username, and `%u' by the username of the user running 76 ssh(1). 77 78 The other keywords' criteria must be single entries or comma- 79 separated lists and may use the wildcard and negation operators 80 described in the PATTERNS section. The criteria for the host 81 keyword are matched against the target hostname, after any 82 substitution by the Hostname option. The originalhost keyword 83 matches against the hostname as it was specified on the command- 84 line. The user keyword matches against the target username on 85 the remote host. The localuser keyword matches against the name 86 of the local user running ssh(1) (this keyword may be useful in 87 system-wide ssh_config files). 88 89 AddressFamily 90 Specifies which address family to use when connecting. Valid 91 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6'' 92 (use IPv6 only). 93 94 BatchMode 95 If set to ``yes'', passphrase/password querying will be disabled. 96 This option is useful in scripts and other batch jobs where no 97 user is present to supply the password. The argument must be 98 ``yes'' or ``no''. The default is ``no''. 99 100 BindAddress 101 Use the specified address on the local machine as the source 102 address of the connection. Only useful on systems with more than 103 one address. Note that this option does not work if 104 UsePrivilegedPort is set to ``yes''. 105 106 CanonicalDomains 107 When CanonicalizeHostname is enabled, this option specifies the 108 list of domain suffixes in which to search for the specified 109 destination host. 110 111 CanonicalizeFallbackLocal 112 Specifies whether to fail with an error when hostname 113 canonicalization fails. The default, ``yes'', will attempt to 114 look up the unqualified hostname using the system resolver's 115 search rules. A value of ``no'' will cause ssh(1) to fail 116 instantly if CanonicalizeHostname is enabled and the target 117 hostname cannot be found in any of the domains specified by 118 CanonicalDomains. 119 120 CanonicalizeHostname 121 Controls whether explicit hostname canonicalization is performed. 122 The default, ``no'', is not to perform any name rewriting and let 123 the system resolver handle all hostname lookups. If set to 124 ``yes'' then, for connections that do not use a ProxyCommand, 125 ssh(1) will attempt to canonicalize the hostname specified on the 126 command line using the CanonicalDomains suffixes and 127 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is 128 set to ``always'', then canonicalization is applied to proxied 129 connections too. 130 131 CanonicalizeMaxDots 132 Specifies the maximum number of dot characters in a hostname 133 before canonicalization is disabled. The default, ``1'', allows 134 a single dot (i.e. hostname.subdomain). 135 136 CanonicalizePermittedCNAMEs 137 Specifies rules to determine whether CNAMEs should be followed 138 when canonicalizing hostnames. The rules consist of one or more 139 arguments of source_domain_list:target_domain_list, where 140 source_domain_list is a pattern-list of domains that may follow 141 CNAMEs in canonicalization, and target_domain_list is a pattern- 142 list of domains that they may resolve to. 143 144 For example, ``*.a.example.com:*.b.example.com,*.c.example.com'' 145 will allow hostnames matching ``*.a.example.com'' to be 146 canonicalized to names in the ``*.b.example.com'' or 147 ``*.c.example.com'' domains. 148 149 ChallengeResponseAuthentication 150 Specifies whether to use challenge-response authentication. The 151 argument to this keyword must be ``yes'' or ``no''. The default 152 is ``yes''. 153 154 CheckHostIP 155 If this flag is set to ``yes'', ssh(1) will additionally check 156 the host IP address in the known_hosts file. This allows ssh to 157 detect if a host key changed due to DNS spoofing. If the option 158 is set to ``no'', the check will not be executed. The default is 159 ``yes''. 160 161 Cipher Specifies the cipher to use for encrypting the session in 162 protocol version 1. Currently, ``blowfish'', ``3des'', and 163 ``des'' are supported. des is only supported in the ssh(1) 164 client for interoperability with legacy protocol 1 165 implementations that do not support the 3des cipher. Its use is 166 strongly discouraged due to cryptographic weaknesses. The 167 default is ``3des''. 168 169 Ciphers 170 Specifies the ciphers allowed for protocol version 2 in order of 171 preference. Multiple ciphers must be comma-separated. The 172 supported ciphers are: 173 174 ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'', 175 ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', 176 ``aes128-gcm@openssh.com'', ``aes256-gcm@openssh.com'', 177 ``arcfour128'', ``arcfour256'', ``arcfour'', ``blowfish-cbc'', 178 ``cast128-cbc'', and ``chacha20-poly1305@openssh.com''. 179 180 The default is: 181 182 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 183 aes128-gcm@openssh.com,aes256-gcm@openssh.com, 184 chacha20-poly1305@openssh.com, 185 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 186 aes256-cbc,arcfour 187 188 The list of available ciphers may also be obtained using the -Q 189 option of ssh(1). 190 191 ClearAllForwardings 192 Specifies that all local, remote, and dynamic port forwardings 193 specified in the configuration files or on the command line be 194 cleared. This option is primarily useful when used from the 195 ssh(1) command line to clear port forwardings set in 196 configuration files, and is automatically set by scp(1) and 197 sftp(1). The argument must be ``yes'' or ``no''. The default is 198 ``no''. 199 200 Compression 201 Specifies whether to use compression. The argument must be 202 ``yes'' or ``no''. The default is ``no''. 203 204 CompressionLevel 205 Specifies the compression level to use if compression is enabled. 206 The argument must be an integer from 1 (fast) to 9 (slow, best). 207 The default level is 6, which is good for most applications. The 208 meaning of the values is the same as in gzip(1). Note that this 209 option applies to protocol version 1 only. 210 211 ConnectionAttempts 212 Specifies the number of tries (one per second) to make before 213 exiting. The argument must be an integer. This may be useful in 214 scripts if the connection sometimes fails. The default is 1. 215 216 ConnectTimeout 217 Specifies the timeout (in seconds) used when connecting to the 218 SSH server, instead of using the default system TCP timeout. 219 This value is used only when the target is down or really 220 unreachable, not when it refuses the connection. 221 222 ControlMaster 223 Enables the sharing of multiple sessions over a single network 224 connection. When set to ``yes'', ssh(1) will listen for 225 connections on a control socket specified using the ControlPath 226 argument. Additional sessions can connect to this socket using 227 the same ControlPath with ControlMaster set to ``no'' (the 228 default). These sessions will try to reuse the master instance's 229 network connection rather than initiating new ones, but will fall 230 back to connecting normally if the control socket does not exist, 231 or is not listening. 232 233 Setting this to ``ask'' will cause ssh to listen for control 234 connections, but require confirmation using the SSH_ASKPASS 235 program before they are accepted (see ssh-add(1) for details). 236 If the ControlPath cannot be opened, ssh will continue without 237 connecting to a master instance. 238 239 X11 and ssh-agent(1) forwarding is supported over these 240 multiplexed connections, however the display and agent forwarded 241 will be the one belonging to the master connection i.e. it is not 242 possible to forward multiple displays or agents. 243 244 Two additional options allow for opportunistic multiplexing: try 245 to use a master connection but fall back to creating a new one if 246 one does not already exist. These options are: ``auto'' and 247 ``autoask''. The latter requires confirmation like the ``ask'' 248 option. 249 250 ControlPath 251 Specify the path to the control socket used for connection 252 sharing as described in the ControlMaster section above or the 253 string ``none'' to disable connection sharing. In the path, `%L' 254 will be substituted by the first component of the local host 255 name, `%l' will be substituted by the local host name (including 256 any domain name), `%h' will be substituted by the target host 257 name, `%n' will be substituted by the original target host name 258 specified on the command line, `%p' the destination port, `%r' by 259 the remote login username, and `%u' by the username of the user 260 running ssh(1). It is recommended that any ControlPath used for 261 opportunistic connection sharing include at least %h, %p, and %r. 262 This ensures that shared connections are uniquely identified. 263 264 ControlPersist 265 When used in conjunction with ControlMaster, specifies that the 266 master connection should remain open in the background (waiting 267 for future client connections) after the initial client 268 connection has been closed. If set to ``no'', then the master 269 connection will not be placed into the background, and will close 270 as soon as the initial client connection is closed. If set to 271 ``yes'', then the master connection will remain in the background 272 indefinitely (until killed or closed via a mechanism such as the 273 ssh(1) ``-O exit'' option). If set to a time in seconds, or a 274 time in any of the formats documented in sshd_config(5), then the 275 backgrounded master connection will automatically terminate after 276 it has remained idle (with no client connections) for the 277 specified time. 278 279 DynamicForward 280 Specifies that a TCP port on the local machine be forwarded over 281 the secure channel, and the application protocol is then used to 282 determine where to connect to from the remote machine. 283 284 The argument must be [bind_address:]port. IPv6 addresses can be 285 specified by enclosing addresses in square brackets. By default, 286 the local port is bound in accordance with the GatewayPorts 287 setting. However, an explicit bind_address may be used to bind 288 the connection to a specific address. The bind_address of 289 ``localhost'' indicates that the listening port be bound for 290 local use only, while an empty address or `*' indicates that the 291 port should be available from all interfaces. 292 293 Currently the SOCKS4 and SOCKS5 protocols are supported, and 294 ssh(1) will act as a SOCKS server. Multiple forwardings may be 295 specified, and additional forwardings can be given on the command 296 line. Only the superuser can forward privileged ports. 297 298 EnableSSHKeysign 299 Setting this option to ``yes'' in the global client configuration 300 file /etc/ssh/ssh_config enables the use of the helper program 301 ssh-keysign(8) during HostbasedAuthentication. The argument must 302 be ``yes'' or ``no''. The default is ``no''. This option should 303 be placed in the non-hostspecific section. See ssh-keysign(8) 304 for more information. 305 306 EscapeChar 307 Sets the escape character (default: `~'). The escape character 308 can also be set on the command line. The argument should be a 309 single character, `^' followed by a letter, or ``none'' to 310 disable the escape character entirely (making the connection 311 transparent for binary data). 312 313 ExitOnForwardFailure 314 Specifies whether ssh(1) should terminate the connection if it 315 cannot set up all requested dynamic, tunnel, local, and remote 316 port forwardings. The argument must be ``yes'' or ``no''. The 317 default is ``no''. 318 319 ForwardAgent 320 Specifies whether the connection to the authentication agent (if 321 any) will be forwarded to the remote machine. The argument must 322 be ``yes'' or ``no''. The default is ``no''. 323 324 Agent forwarding should be enabled with caution. Users with the 325 ability to bypass file permissions on the remote host (for the 326 agent's Unix-domain socket) can access the local agent through 327 the forwarded connection. An attacker cannot obtain key material 328 from the agent, however they can perform operations on the keys 329 that enable them to authenticate using the identities loaded into 330 the agent. 331 332 ForwardX11 333 Specifies whether X11 connections will be automatically 334 redirected over the secure channel and DISPLAY set. The argument 335 must be ``yes'' or ``no''. The default is ``no''. 336 337 X11 forwarding should be enabled with caution. Users with the 338 ability to bypass file permissions on the remote host (for the 339 user's X11 authorization database) can access the local X11 340 display through the forwarded connection. An attacker may then 341 be able to perform activities such as keystroke monitoring if the 342 ForwardX11Trusted option is also enabled. 343 344 ForwardX11Timeout 345 Specify a timeout for untrusted X11 forwarding using the format 346 described in the TIME FORMATS section of sshd_config(5). X11 347 connections received by ssh(1) after this time will be refused. 348 The default is to disable untrusted X11 forwarding after twenty 349 minutes has elapsed. 350 351 ForwardX11Trusted 352 If this option is set to ``yes'', remote X11 clients will have 353 full access to the original X11 display. 354 355 If this option is set to ``no'', remote X11 clients will be 356 considered untrusted and prevented from stealing or tampering 357 with data belonging to trusted X11 clients. Furthermore, the 358 xauth(1) token used for the session will be set to expire after 359 20 minutes. Remote clients will be refused access after this 360 time. 361 362 The default is ``no''. 363 364 See the X11 SECURITY extension specification for full details on 365 the restrictions imposed on untrusted clients. 366 367 GatewayPorts 368 Specifies whether remote hosts are allowed to connect to local 369 forwarded ports. By default, ssh(1) binds local port forwardings 370 to the loopback address. This prevents other remote hosts from 371 connecting to forwarded ports. GatewayPorts can be used to 372 specify that ssh should bind local port forwardings to the 373 wildcard address, thus allowing remote hosts to connect to 374 forwarded ports. The argument must be ``yes'' or ``no''. The 375 default is ``no''. 376 377 GlobalKnownHostsFile 378 Specifies one or more files to use for the global host key 379 database, separated by whitespace. The default is 380 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2. 381 382 GSSAPIAuthentication 383 Specifies whether user authentication based on GSSAPI is allowed. 384 The default is ``no''. Note that this option applies to protocol 385 version 2 only. 386 387 GSSAPIDelegateCredentials 388 Forward (delegate) credentials to the server. The default is 389 ``no''. Note that this option applies to protocol version 2 390 only. 391 392 HashKnownHosts 393 Indicates that ssh(1) should hash host names and addresses when 394 they are added to ~/.ssh/known_hosts. These hashed names may be 395 used normally by ssh(1) and sshd(8), but they do not reveal 396 identifying information should the file's contents be disclosed. 397 The default is ``no''. Note that existing names and addresses in 398 known hosts files will not be converted automatically, but may be 399 manually hashed using ssh-keygen(1). 400 401 HostbasedAuthentication 402 Specifies whether to try rhosts based authentication with public 403 key authentication. The argument must be ``yes'' or ``no''. The 404 default is ``no''. This option applies to protocol version 2 405 only and is similar to RhostsRSAAuthentication. 406 407 HostKeyAlgorithms 408 Specifies the protocol version 2 host key algorithms that the 409 client wants to use in order of preference. The default for this 410 option is: 411 412 ecdsa-sha2-nistp256-cert-v01@openssh.com, 413 ecdsa-sha2-nistp384-cert-v01@openssh.com, 414 ecdsa-sha2-nistp521-cert-v01@openssh.com, 415 ssh-ed25519-cert-v01@openssh.com, 416 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, 417 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, 418 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 419 ssh-ed25519,ssh-rsa,ssh-dss 420 421 If hostkeys are known for the destination host then this default 422 is modified to prefer their algorithms. 423 424 HostKeyAlias 425 Specifies an alias that should be used instead of the real host 426 name when looking up or saving the host key in the host key 427 database files. This option is useful for tunneling SSH 428 connections or for multiple servers running on a single host. 429 430 HostName 431 Specifies the real host name to log into. This can be used to 432 specify nicknames or abbreviations for hosts. If the hostname 433 contains the character sequence `%h', then this will be replaced 434 with the host name specified on the command line (this is useful 435 for manipulating unqualified names). The default is the name 436 given on the command line. Numeric IP addresses are also 437 permitted (both on the command line and in HostName 438 specifications). 439 440 IdentitiesOnly 441 Specifies that ssh(1) should only use the authentication identity 442 files configured in the ssh_config files, even if ssh-agent(1) or 443 a PKCS11Provider offers more identities. The argument to this 444 keyword must be ``yes'' or ``no''. This option is intended for 445 situations where ssh-agent offers many different identities. The 446 default is ``no''. 447 448 IdentityFile 449 Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA 450 authentication identity is read. The default is ~/.ssh/identity 451 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, 452 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2. 453 Additionally, any identities represented by the authentication 454 agent will be used for authentication unless IdentitiesOnly is 455 set. ssh(1) will try to load certificate information from the 456 filename obtained by appending -cert.pub to the path of a 457 specified IdentityFile. 458 459 The file name may use the tilde syntax to refer to a user's home 460 directory or one of the following escape characters: `%d' (local 461 user's home directory), `%u' (local user name), `%l' (local host 462 name), `%h' (remote host name) or `%r' (remote user name). 463 464 It is possible to have multiple identity files specified in 465 configuration files; all these identities will be tried in 466 sequence. Multiple IdentityFile directives will add to the list 467 of identities tried (this behaviour differs from that of other 468 configuration directives). 469 470 IdentityFile may be used in conjunction with IdentitiesOnly to 471 select which identities in an agent are offered during 472 authentication. 473 474 IgnoreUnknown 475 Specifies a pattern-list of unknown options to be ignored if they 476 are encountered in configuration parsing. This may be used to 477 suppress errors if ssh_config contains options that are 478 unrecognised by ssh(1). It is recommended that IgnoreUnknown be 479 listed early in the configuration file as it will not be applied 480 to unknown options that appear before it. 481 482 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections. 483 Accepted values are ``af11'', ``af12'', ``af13'', ``af21'', 484 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'', 485 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'', 486 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'', 487 ``reliability'', or a numeric value. This option may take one or 488 two arguments, separated by whitespace. If one argument is 489 specified, it is used as the packet class unconditionally. If 490 two values are specified, the first is automatically selected for 491 interactive sessions and the second for non-interactive sessions. 492 The default is ``lowdelay'' for interactive sessions and 493 ``throughput'' for non-interactive sessions. 494 495 KbdInteractiveAuthentication 496 Specifies whether to use keyboard-interactive authentication. 497 The argument to this keyword must be ``yes'' or ``no''. The 498 default is ``yes''. 499 500 KbdInteractiveDevices 501 Specifies the list of methods to use in keyboard-interactive 502 authentication. Multiple method names must be comma-separated. 503 The default is to use the server specified list. The methods 504 available vary depending on what the server supports. For an 505 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'', 506 and ``skey''. 507 508 KexAlgorithms 509 Specifies the available KEX (Key Exchange) algorithms. Multiple 510 algorithms must be comma-separated. The default is: 511 512 curve25519-sha256@libssh.org, 513 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 514 diffie-hellman-group-exchange-sha256, 515 diffie-hellman-group-exchange-sha1, 516 diffie-hellman-group14-sha1, 517 diffie-hellman-group1-sha1 518 519 LocalCommand 520 Specifies a command to execute on the local machine after 521 successfully connecting to the server. The command string 522 extends to the end of the line, and is executed with the user's 523 shell. The following escape character substitutions will be 524 performed: `%d' (local user's home directory), `%h' (remote host 525 name), `%l' (local host name), `%n' (host name as provided on the 526 command line), `%p' (remote port), `%r' (remote user name) or 527 `%u' (local user name). 528 529 The command is run synchronously and does not have access to the 530 session of the ssh(1) that spawned it. It should not be used for 531 interactive commands. 532 533 This directive is ignored unless PermitLocalCommand has been 534 enabled. 535 536 LocalForward 537 Specifies that a TCP port on the local machine be forwarded over 538 the secure channel to the specified host and port from the remote 539 machine. The first argument must be [bind_address:]port and the 540 second argument must be host:hostport. IPv6 addresses can be 541 specified by enclosing addresses in square brackets. Multiple 542 forwardings may be specified, and additional forwardings can be 543 given on the command line. Only the superuser can forward 544 privileged ports. By default, the local port is bound in 545 accordance with the GatewayPorts setting. However, an explicit 546 bind_address may be used to bind the connection to a specific 547 address. The bind_address of ``localhost'' indicates that the 548 listening port be bound for local use only, while an empty 549 address or `*' indicates that the port should be available from 550 all interfaces. 551 552 LogLevel 553 Gives the verbosity level that is used when logging messages from 554 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, 555 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 556 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 557 higher levels of verbose output. 558 559 MACs Specifies the MAC (message authentication code) algorithms in 560 order of preference. The MAC algorithm is used in protocol 561 version 2 for data integrity protection. Multiple algorithms 562 must be comma-separated. The algorithms that contain ``-etm'' 563 calculate the MAC after encryption (encrypt-then-mac). These are 564 considered safer and their use recommended. The default is: 565 566 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, 567 umac-64-etm@openssh.com,umac-128-etm@openssh.com, 568 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, 569 hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com, 570 hmac-md5-96-etm@openssh.com, 571 hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com, 572 hmac-sha2-256,hmac-sha2-512,hmac-ripemd160, 573 hmac-sha1-96,hmac-md5-96 574 575 NoHostAuthenticationForLocalhost 576 This option can be used if the home directory is shared across 577 machines. In this case localhost will refer to a different 578 machine on each of the machines and the user will get many 579 warnings about changed host keys. However, this option disables 580 host authentication for localhost. The argument to this keyword 581 must be ``yes'' or ``no''. The default is to check the host key 582 for localhost. 583 584 NumberOfPasswordPrompts 585 Specifies the number of password prompts before giving up. The 586 argument to this keyword must be an integer. The default is 3. 587 588 PasswordAuthentication 589 Specifies whether to use password authentication. The argument 590 to this keyword must be ``yes'' or ``no''. The default is 591 ``yes''. 592 593 PermitLocalCommand 594 Allow local command execution via the LocalCommand option or 595 using the !command escape sequence in ssh(1). The argument must 596 be ``yes'' or ``no''. The default is ``no''. 597 598 PKCS11Provider 599 Specifies which PKCS#11 provider to use. The argument to this 600 keyword is the PKCS#11 shared library ssh(1) should use to 601 communicate with a PKCS#11 token providing the user's private RSA 602 key. 603 604 Port Specifies the port number to connect on the remote host. The 605 default is 22. 606 607 PreferredAuthentications 608 Specifies the order in which the client should try protocol 2 609 authentication methods. This allows a client to prefer one 610 method (e.g. keyboard-interactive) over another method (e.g. 611 password). The default is: 612 613 gssapi-with-mic,hostbased,publickey, 614 keyboard-interactive,password 615 616 Protocol 617 Specifies the protocol versions ssh(1) should support in order of 618 preference. The possible values are `1' and `2'. Multiple 619 versions must be comma-separated. When this option is set to 620 ``2,1'' ssh will try version 2 and fall back to version 1 if 621 version 2 is not available. The default is `2'. 622 623 ProxyCommand 624 Specifies the command to use to connect to the server. The 625 command string extends to the end of the line, and is executed 626 with the user's shell. In the command string, any occurrence of 627 `%h' will be substituted by the host name to connect, `%p' by the 628 port, and `%r' by the remote user name. The command can be 629 basically anything, and should read from its standard input and 630 write to its standard output. It should eventually connect an 631 sshd(8) server running on some machine, or execute sshd -i 632 somewhere. Host key management will be done using the HostName 633 of the host being connected (defaulting to the name typed by the 634 user). Setting the command to ``none'' disables this option 635 entirely. Note that CheckHostIP is not available for connects 636 with a proxy command. 637 638 This directive is useful in conjunction with nc(1) and its proxy 639 support. For example, the following directive would connect via 640 an HTTP proxy at 192.0.2.0: 641 642 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 643 644 ProxyUseFdpass 645 Specifies that ProxyCommand will pass a connected file descriptor 646 back to ssh(1) instead of continuing to execute and pass data. 647 The default is ``no''. 648 649 PubkeyAuthentication 650 Specifies whether to try public key authentication. The argument 651 to this keyword must be ``yes'' or ``no''. The default is 652 ``yes''. This option applies to protocol version 2 only. 653 654 RekeyLimit 655 Specifies the maximum amount of data that may be transmitted 656 before the session key is renegotiated, optionally followed a 657 maximum amount of time that may pass before the session key is 658 renegotiated. The first argument is specified in bytes and may 659 have a suffix of `K', `M', or `G' to indicate Kilobytes, 660 Megabytes, or Gigabytes, respectively. The default is between 661 `1G' and `4G', depending on the cipher. The optional second 662 value is specified in seconds and may use any of the units 663 documented in the TIME FORMATS section of sshd_config(5). The 664 default value for RekeyLimit is ``default none'', which means 665 that rekeying is performed after the cipher's default amount of 666 data has been sent or received and no time based rekeying is 667 done. This option applies to protocol version 2 only. 668 669 RemoteForward 670 Specifies that a TCP port on the remote machine be forwarded over 671 the secure channel to the specified host and port from the local 672 machine. The first argument must be [bind_address:]port and the 673 second argument must be host:hostport. IPv6 addresses can be 674 specified by enclosing addresses in square brackets. Multiple 675 forwardings may be specified, and additional forwardings can be 676 given on the command line. Privileged ports can be forwarded 677 only when logging in as root on the remote machine. 678 679 If the port argument is `0', the listen port will be dynamically 680 allocated on the server and reported to the client at run time. 681 682 If the bind_address is not specified, the default is to only bind 683 to loopback addresses. If the bind_address is `*' or an empty 684 string, then the forwarding is requested to listen on all 685 interfaces. Specifying a remote bind_address will only succeed 686 if the server's GatewayPorts option is enabled (see 687 sshd_config(5)). 688 689 RequestTTY 690 Specifies whether to request a pseudo-tty for the session. The 691 argument may be one of: ``no'' (never request a TTY), ``yes'' 692 (always request a TTY when standard input is a TTY), ``force'' 693 (always request a TTY) or ``auto'' (request a TTY when opening a 694 login session). This option mirrors the -t and -T flags for 695 ssh(1). 696 697 RhostsRSAAuthentication 698 Specifies whether to try rhosts based authentication with RSA 699 host authentication. The argument must be ``yes'' or ``no''. 700 The default is ``no''. This option applies to protocol version 1 701 only and requires ssh(1) to be setuid root. 702 703 RSAAuthentication 704 Specifies whether to try RSA authentication. The argument to 705 this keyword must be ``yes'' or ``no''. RSA authentication will 706 only be attempted if the identity file exists, or an 707 authentication agent is running. The default is ``yes''. Note 708 that this option applies to protocol version 1 only. 709 710 SendEnv 711 Specifies what variables from the local environ(7) should be sent 712 to the server. Note that environment passing is only supported 713 for protocol 2. The server must also support it, and the server 714 must be configured to accept these environment variables. Refer 715 to AcceptEnv in sshd_config(5) for how to configure the server. 716 Variables are specified by name, which may contain wildcard 717 characters. Multiple environment variables may be separated by 718 whitespace or spread across multiple SendEnv directives. The 719 default is not to send any environment variables. 720 721 See PATTERNS for more information on patterns. 722 723 ServerAliveCountMax 724 Sets the number of server alive messages (see below) which may be 725 sent without ssh(1) receiving any messages back from the server. 726 If this threshold is reached while server alive messages are 727 being sent, ssh will disconnect from the server, terminating the 728 session. It is important to note that the use of server alive 729 messages is very different from TCPKeepAlive (below). The server 730 alive messages are sent through the encrypted channel and 731 therefore will not be spoofable. The TCP keepalive option 732 enabled by TCPKeepAlive is spoofable. The server alive mechanism 733 is valuable when the client or server depend on knowing when a 734 connection has become inactive. 735 736 The default value is 3. If, for example, ServerAliveInterval 737 (see below) is set to 15 and ServerAliveCountMax is left at the 738 default, if the server becomes unresponsive, ssh will disconnect 739 after approximately 45 seconds. This option applies to protocol 740 version 2 only. 741 742 ServerAliveInterval 743 Sets a timeout interval in seconds after which if no data has 744 been received from the server, ssh(1) will send a message through 745 the encrypted channel to request a response from the server. The 746 default is 0, indicating that these messages will not be sent to 747 the server. This option applies to protocol version 2 only. 748 749 StrictHostKeyChecking 750 If this flag is set to ``yes'', ssh(1) will never automatically 751 add host keys to the ~/.ssh/known_hosts file, and refuses to 752 connect to hosts whose host key has changed. This provides 753 maximum protection against trojan horse attacks, though it can be 754 annoying when the /etc/ssh/ssh_known_hosts file is poorly 755 maintained or when connections to new hosts are frequently made. 756 This option forces the user to manually add all new hosts. If 757 this flag is set to ``no'', ssh will automatically add new host 758 keys to the user known hosts files. If this flag is set to 759 ``ask'', new host keys will be added to the user known host files 760 only after the user has confirmed that is what they really want 761 to do, and ssh will refuse to connect to hosts whose host key has 762 changed. The host keys of known hosts will be verified 763 automatically in all cases. The argument must be ``yes'', 764 ``no'', or ``ask''. The default is ``ask''. 765 766 TCPKeepAlive 767 Specifies whether the system should send TCP keepalive messages 768 to the other side. If they are sent, death of the connection or 769 crash of one of the machines will be properly noticed. However, 770 this means that connections will die if the route is down 771 temporarily, and some people find it annoying. 772 773 The default is ``yes'' (to send TCP keepalive messages), and the 774 client will notice if the network goes down or the remote host 775 dies. This is important in scripts, and many users want it too. 776 777 To disable TCP keepalive messages, the value should be set to 778 ``no''. 779 780 Tunnel Request tun(4) device forwarding between the client and the 781 server. The argument must be ``yes'', ``point-to-point'' (layer 782 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes'' 783 requests the default tunnel mode, which is ``point-to-point''. 784 The default is ``no''. 785 786 TunnelDevice 787 Specifies the tun(4) devices to open on the client (local_tun) 788 and the server (remote_tun). 789 790 The argument must be local_tun[:remote_tun]. The devices may be 791 specified by numerical ID or the keyword ``any'', which uses the 792 next available tunnel device. If remote_tun is not specified, it 793 defaults to ``any''. The default is ``any:any''. 794 795 UsePrivilegedPort 796 Specifies whether to use a privileged port for outgoing 797 connections. The argument must be ``yes'' or ``no''. The 798 default is ``no''. If set to ``yes'', ssh(1) must be setuid 799 root. Note that this option must be set to ``yes'' for 800 RhostsRSAAuthentication with older servers. 801 802 User Specifies the user to log in as. This can be useful when a 803 different user name is used on different machines. This saves 804 the trouble of having to remember to give the user name on the 805 command line. 806 807 UserKnownHostsFile 808 Specifies one or more files to use for the user host key 809 database, separated by whitespace. The default is 810 ~/.ssh/known_hosts, ~/.ssh/known_hosts2. 811 812 VerifyHostKeyDNS 813 Specifies whether to verify the remote key using DNS and SSHFP 814 resource records. If this option is set to ``yes'', the client 815 will implicitly trust keys that match a secure fingerprint from 816 DNS. Insecure fingerprints will be handled as if this option was 817 set to ``ask''. If this option is set to ``ask'', information on 818 fingerprint match will be displayed, but the user will still need 819 to confirm new host keys according to the StrictHostKeyChecking 820 option. The argument must be ``yes'', ``no'', or ``ask''. The 821 default is ``no''. Note that this option applies to protocol 822 version 2 only. 823 824 See also VERIFYING HOST KEYS in ssh(1). 825 826 VisualHostKey 827 If this flag is set to ``yes'', an ASCII art representation of 828 the remote host key fingerprint is printed in addition to the hex 829 fingerprint string at login and for unknown host keys. If this 830 flag is set to ``no'', no fingerprint strings are printed at 831 login and only the hex fingerprint string will be printed for 832 unknown host keys. The default is ``no''. 833 834 XAuthLocation 835 Specifies the full pathname of the xauth(1) program. The default 836 is /usr/X11R6/bin/xauth. 837 838PATTERNS 839 A pattern consists of zero or more non-whitespace characters, `*' (a 840 wildcard that matches zero or more characters), or `?' (a wildcard that 841 matches exactly one character). For example, to specify a set of 842 declarations for any host in the ``.co.uk'' set of domains, the following 843 pattern could be used: 844 845 Host *.co.uk 846 847 The following pattern would match any host in the 192.168.0.[0-9] network 848 range: 849 850 Host 192.168.0.? 851 852 A pattern-list is a comma-separated list of patterns. Patterns within 853 pattern-lists may be negated by preceding them with an exclamation mark 854 (`!'). For example, to allow a key to be used from anywhere within an 855 organization except from the ``dialup'' pool, the following entry (in 856 authorized_keys) could be used: 857 858 from="!*.dialup.example.com,*.example.com" 859 860FILES 861 ~/.ssh/config 862 This is the per-user configuration file. The format of this file 863 is described above. This file is used by the SSH client. 864 Because of the potential for abuse, this file must have strict 865 permissions: read/write for the user, and not accessible by 866 others. 867 868 /etc/ssh/ssh_config 869 Systemwide configuration file. This file provides defaults for 870 those values that are not specified in the user's configuration 871 file, and for those users who do not have a configuration file. 872 This file must be world-readable. 873 874SEE ALSO 875 ssh(1) 876 877AUTHORS 878 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 879 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 880 de Raadt and Dug Song removed many bugs, re-added newer features and 881 created OpenSSH. Markus Friedl contributed the support for SSH protocol 882 versions 1.5 and 2.0. 883 884OpenBSD 5.4 January 19, 2014 OpenBSD 5.4 885